By
John Baechtel May 17, 2018The process of hard anodizing is broadly employed across numerous commercial industries. It is a highly effective surface treatment when industrial parts are exposed to high corrosion or aggressive wear environments where component integrity and dimensional stability are essential. Anodizing is a well-established metal impregnating process with primary application on two fronts; one that enhances the appearance of various metal components in a decorative sense and another that improves the wear characteristics and corrosion resistance of said parts to ensure top performance. The process is similar for both, differing primarily in the thickness of the coating, the process used to achieve it and, of course, the reason for applying it.
All of Diamond’s forged aluminum diesel pistons are treated to hard anodizing to prepare them for the rigors of that high cylinder pressure, high-boost environment.
Hard anodizing is applied to high performance pistons to enhance component integrity in critical areas like the ring lands and the piston skirts. Type 3 anodizing, or hardcoating, plays an important role in combating microwelding between the ring grooves and the piston rings. Microwelding is a form of localized component welding characterized by the separation and transference of piston material from the piston ring groove to the underside of the piston ring. It is a form of friction welding caused by high temperature and excessive movement in the ring groove. Ring seal at the cylinder wall is only as good as the seal at the bottom of the ring groove under combustion pressure. When temperatures are high, and the clearance is incorrect, microwelding can occur and proper sealing suffers.
Diamond’s hard anodized and moly dry-film coated race pistons are precision parts with jewel-like appearance and robust durability and performance. This unique combination of performance coatings assures top quality and the trouble-free performance you are seeking.
When microwelding happens, it restricts the free movement and rotation of the piston ring and can ultimately jam the ring in its groove, causing a rise in blowby and increasing the potential for detonation. Over time the ring groove can flair, increasing clearance and further destabilizing ring movement and function. Hard anodizing toughens ring grooves and resists the undesirable transfer of material to the bottom of the ring and its destabilizing effects.
Diamond Pistons have pursued a robust program of providing high quality ring grooves in its pistons, both dimensionally and in terms of surface finish and resistance to the effects of microwelding. Hard anodizing is an essential component of those efforts.
ExceptionsHard anodizing also affects heat transfer. While it is broadly understood that heat transfers to the cylinder walls and thus the cooling system via the ring interface, heat also transfers through the skirts. There are differing schools of thought, primarily addressing final application. On one hand, it is desirable to retain heat in the combustion chamber to support greater power and efficiency. That’s particularly true in shorter-duration drag racing applications. It can also be true for longer duration applications such as sprint cars, Cup cars and naturally-aspirated road racing applications, provided that the engine builder is comfortable with the necessary increase in piston to wall clearance.